Air bag inflator using liquid monopropellant and adaptable to produce ouputs with various parameters

ABSTRACT

A gas generator to provide gases under pressure to inflate a vehicular air bag. A capsular enclosure contains a fluid gas-generating charge. The enclosure has a non-pyrotechnic initiator, a frangible wall portion, and a chamber with a major portion of its volume on the other side of the frangible wall portion from the initiator. Various chamber and nozzle configurations provide for different initial pressures and temperatures, and times from maximum pressure or ambient pressure. Successive bursts are possible.

CROSS-REFERENCE TO OTHER PATENT APPLICATION

This is a continuation-in part of applicants' co-pending U.S. patentapplication Ser. No. 08/332,415, filed Oct. 31, 1994, entitled "Inflatorfor Vehicular Air Bags".

FIELD OF THE INVENTION

An inflator for vehicle air bags which uses a liquid monopropellant andwhich can be adapted to produce outputs of gas with various parametersof pressure, temperature, and flow rates.

BACKGROUND OF THE INVENTION

Air bags which inflate upon impact to protect passengers in vehicleshave become standard safety items. Their inflators must be inherentlystable for long shelf life, and readily and reliably be initiatiable soas to generate and release a substantial volume of gas at a prescribedpressure very quickly, in fact in small fractions of a second.

It is known to store gas for this purpose at a high pressure to releaseupon impact. The long-term storage of high pressure gas, and theconsequences of an unintended breach of its container are distinctdrawbacks to such arrangements. Instead the preference is to utilize achemical charge which, when initiated will release gas in the desiredvolume and at the requisite pressure. Currently the preference for sucha charge is a solid. The known solids generally generate gases andresidues which are toxic, or at best are environmentally undesirable.

The disadvantages of both of these charges are well-known. The gasbottle is carried as a potential risk both during the lifetime of theautomobile and when the vehicle is scrapped. If the wrecker has notremoved the bottle, and inadvertently cuts it, an explosive situationcould occur without his foreknowledge. It is both a physical threat offlying objects, and/or a fire threat, because its content may catch onfire.

The solid charges involve the risks to the wrecker that he may initiatethe charge without knowing it, incurring exposure to a toxic substanceor of spilling a dangerous substance. The solid products are generallynot environmentally suitable, and can readily be ignited.

Further, there are substantial risks inherent in the manufacture of thesolid propellent, such as are commonly used for solid gas-generatingcharges. These charges, often azides, are tabletted in munitions-gradefacilities, and have their share of accidents, many of them fatal. Thevery property that makes these products suitable for air baginflation--quick reaction to generate high temperatures gases is alsothe property which makes them risky to process.

It has only recently become appreciated that a liquid charge can be evenmore effective for gas generation than a solid charge, and that some ofthe above risks inherent in the use of a solid charge and compressedgases can be overcome. In fact an inflator according to this inventioncan eliminate all of them.

However, the earlier efforts to use liquid charges that are known to theinventors herein have required complicated apparatus, and chemicalignition charges that are initiated by still another initiator to setthem off. Movable gas control means in them such as pistons are the normto control the gas-generation reaction and to keep it "burning".

For example, Giovanetti U.S. Pat. No. 5,060,973 utilizes a liquidpropellant--a hydroxyl ammonium nitrate-based propellant, which isignited by a pyrotechnic igniter, such as, smokeless powder set off byan electric primer like an exploding bridge wire. In order to ignite thegas-generating charge in the device, the products of composition of thepyrotechnic igniter must be discharged into it, and in a controlledmanner. This requires a movable piston to separate the main charge fromthe igniter charge, and separate channel means to convey the ignitedgases into a reaction chamber while the piston gradually forces the maincharge into the reaction chamber.

This is a relatively complicated arrangement, and friction, degradationor destruction of the piston would be expected to lead to an uncertainoutput. Furthermore, the propellant compound if it leaked (duringscrapping of the vehicle, for example) would contaminate thesurroundings. In addition, the black powder charge would still bepresent as a risk to setting off the main charge.

Brede U.S. Pat. No. 5,030,730 utilizes a liquified gas--a short chainhydrocarbon such as propane, in combination with nitrous oxide (N2O). Toignite this charge, a pyrotechnic igniter is also used to propel apenetrator piston to puncture the container. The piston carries two setsof channels. One is to carry igniter gas into the storage chamber, andthe other is to carry them to a chamber from which the hot gases enterthe air bag. In some of his embodiments he keeps his components inseparate chambers, and the piston has the additional function ofenabling the two components to mix. Then the piston is also required topierce the two chambers.

The hazards that accompany a stored charge of liquified gas underpressure have been described above, and are found in this construction.Also it requires a movable piston to open the storage chamber orchambers and to regulate and direct the flow of the liquids. Suchcomplications are undesirable in a critical man-safety device.

It is the object of this invention to provide an inflator which requiresno moving parts, which even though its charge is under moderate pressureconstitutes no storage or scrapping risk, which does not requirepyrotechnic means for the charge itself or for its ignition, whosecharge composition is environmentally benign, and which can bemanufactured, stored and scrapped with no or negligible risk toequipment, facilities, or human life.

The charge of this invention is a liquid monopropellant. As the term"monopropellant" is used herein it means a compound or a mixture ofcompounds which are stored mixed together, and which, when initiated,involves no addition of other substances to generate the gases.

The use of a liquid monopropellant offers advantages not readilyattainable with solid charges and/or hybrid inflators. For example bymodifications of the chamber or chambers in which the liquid is storedand combusted (which often is the same chamber), an inflator can beadapted to produce gases at different temperatures, pressures, flowrates, rates of pressure rise, and multiple pulses.

The structures involved are elegantly simple and are highly reliable. Itis even possible to adapt such structures to produce sequential pulsesof gas triggered by a second impact, or to accommodate such variables asheavier passengers who might require a higher rise rate of gas pressure.

It is another object of this invention to provide such an inflator whoseinitiator means is unsensitive to stray electrical charges orinterference.

It is another object of this invention to provide an inflator with theforegoing advantages among others.

BRIEF DESCRIPTION OF THE INVENTION

An air bag inflator according to this invention utilizes for its sourceof gas a liquid monopropellant comprising nitrous oxide and a liquidalcohol. The mixture of these chemicals will involve some of the nitrousoxide being dissolved in the alcohol, and some of it being in thegaseous phase. Depending on the temperature and pressure, some of thenitrous oxide may instead or also be in the liquid phase. The mixturewhen stored will be at an elevated pressure, and at an ambienttemperature relative to the location where the inflator is mounted.

According to a preferred embodiment of the invention, the liquidcomponent is a primary or secondary alcohol of a saturated open-chainhydrocarbon (alkane series), with carbon between 1 and 4, preferablyethyl alcohol, and the gaseous component is nitrous oxide (N2O). Ethylalcohol has the advantage that it is a "green" substance which isbiodegradable and can freely be discharged into the environment withoutrisk.

The mixture of liquid and gas components is stored under suitablepressure in a reaction chamber to increase the amount of N2O in thecharge.

The reaction chamber is fitted with a passive ignition device which maybe an electrical igniter, or less preferably a chemical ignition meansset off by an electrical current, or a laser beam. The wall of thereaction chamber includes frangible portions that are opened by pressuregenerated by generated gases to form discharge ports.

Preferably, but not necessarily, the hot gases flow through an expansionchamber in which any incompleted combustion is completed and the gasesare cooled. They then flow into the air bag. Conveniently, baffles maybe provided in the expansion chamber to regulate the flow of the gases,and to some extent to control the rate of reaction in the reactionchamber.

The charge is stored in a closed chamber which is constructed towithstand a storage pressure and also the higher pressures which will begenerated when the charge is initiated. An initiator is disposed in thecombustion chamber.

The combustion chamber wall includes a burst portion which will rupturewhen a sufficient internal pressure is generated by the charge.

According to one embodiment of the invention, there is no restriction ofthe flow of generated gases to the burst portion. As will later beshown, this results in a lower pressure, higher temperature gas output.This embodiment is sometimes called a "low pressure-high temperature"device.

According to another embodiment of the invention, a nozzle is placed inthe combustion chamber between the burst portion and the major volume ofthe combustion chamber. As will later be shown, this results in arestricted flow through the nozzle. While the combustion chamberpressure upstream of the nozzle is higher, the output temperature islower. This embodiment is sometimes called a "high pressure-lowtemperature" device.

According to a preferred but optional feature of the invention, anauxiliary combustion chamber can be provided which is separatelyinitiated in order to provide for multiple bursts of pressure, therebyproviding a different pressure rise rate, or a later burst in responseto events subsequent to the first event.

The above and other features of this invention will be fully understoodfrom the following detailed description and the accompanying drawings,in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the performance features of this invention;

FIG. 2 is a view partly in cutaway cross-section showing a simplifiedembodiment of the invention;

FIG. 3 is a similar view showing another simplified embodiment of theinvention;

FIG. 4 is a similar view showing yet another simplified embodiment ofthe invention;

FIG. 5 is a semi-schematic showing of another simplified embodimentincorporating a plurality of combustion chambers;

FIG. 6 is a schematic showing of the presently-preferred systemadaptable to either of the regimes;

FIG. 7 is a schematic showing an embodiment of a multi-burst device;

FIG. 8 is an axial cross-section of the presently-preferred embodimentof the invention;

FIG. 9 is a top view taken in FIG. 8;

FIG. 10 is an enlarged portion of FIG. 8;

FIG. 11 is an axial cross-section of another embodiment of theinvention; and

FIG. 12 is a bottom view taken in FIG. 11.

DETAILED DESCRIPTION OF THE INVENTION

An understanding of this invention will be facilitated by an initialconsideration of the parameters appropriate to the inflation of an airbag by this inflator. An air bag which is provided to protect passengersin a vehicle upon impact must react very quickly. A person brought to anabrupt stop in a speeding vehicle must be restrained against contactwith the vehicle and protected against strong impact with it, and heldfor the few brief moments in which the violent motions continue. Thesame considerations are true for side impacts, where a speeding vehiclestrikes another broadside, and also for conditions which arise when avehicle rolls or tumbles. All of these circumstances require an almostimmediate inflation of the air bag to a sufficient pressure to hold theperson in place, but not so high that the air bag itself would injurethe person.

This involves the generation or supply of gas at an initial highpressure outside of the bag in order immediately to provide a sufficientvolume of gas, the reduction of this pressure to the desired value forthe bag--usually about 45 psia--and reduction of the temperature of thegases to a suitable value which will not harm the material of the bag orinjure the person being protected.

FIG. 1 schematically illustrates the interplay of these parameters. Inthis graph, traces 11, 12 and 13 exemplify several regimes availablewith this invention. The abscissa is the temperature of the gas, and theordinate is the pressure of the gas. The traces further represent a timedimension, reading from right to left along the abscissa. The length ofthe trace is directly proportional to the time involved; for example,trace 11 represents a longer time than either trace 12 or 13.

The right-hand ends of the traces represent the initial high pressuregenerated in the combustion chamber during combustion. The traces followfrom their right hand end to the ultimate air bag pressure at theirleft-hand end. For every trace, this air bag pressure is 45 psia. Itwill be observed that the temperature of the gas at the air bag pressurediffers remarkably between the traces and the parameters andconstructions which they reflect.

It is of interest to observe that this inflator, when adapted to operateon the regime of trace 11 where the initial chamber pressure is muchhigher reaches the working pressure at an appreciably lower temperaturethan the regime denoted by traces 12 and 13, where the initial chamberpressures are lower. There are substantial advantages to each of theseregimes, and this invention enables the designer to adapt the structureand charge to provide the most advantageous regime for a giveninstallation.

The traces are generalized for convenience in disclosure.

Before discussing the gas-generating charge in detail a further generalobservation will illustrate the superiority of this liquid charge over asolid charge. In this invention there need be no separate initiatorcharge, although a chemical squib could be provided if desired. Allignition occurs primarily in the combustion chamber and withoutnecessary participation by any other substance, such as hot gases froman initiator charge (although one can be utilized if desired). Afterbeing initiated the reaction of the charge is self-sustaining. Further,because there is a substantial length of charge from the initiator, andthe burst port is close to the initiator, the combustion face of thecharge will recede from the initiator and from the burst port. Thegaseous products will exit through the burst port and no liquid will beexpelled to require reaction beyond the burst port. The charge whenstored is under pressure. After initiation, the pressure in the chamber(and charge) greatly increases. Therefore no means is needed to expelthe liquid charge and the combustion products, because the reactionchamber is closed beyond the burst port and the chamber pressure expelsthe products of combustion.

Accordingly, in contrast to other known devices that use liquid charges,it is intended that reaction primarily occur in the chamber where thecharge is stored. This significantly reduces the bulk and complexity ofthe device, because it is not necessary to provide a substantial volumein which reaction is to occur downstream from the storage means.

While nitrous oxide is significantly soluble in ethyl alcohol, forexample, a greater molar proportion of this gas relative to the alcoholis to be preferred than the proportion of the dissolved gas to thealcohol at standard temperatures and pressures. This can readily beaccomplished by increasing the pressure under which the combination ofthese two components is stored. Of course under pressure there is to beexpected some supernatant gas, but much of the nitrous oxide will bedissolved in the alcohol. This is a considerable advantage to thisinvention, because the reactants will be so fully mixed prior toinitiation.

In addition, because the liquid component of the charge will always bein the liquid phase at the temperatures and pressures anticipated to beencountered in storage, and because the critical temperatures andpressures of nitrous oxide are such that at some of the temperatures andpressures to be encountered, nitrous oxide in excess of that which candissolve may be in the gas phase, it is to be understood that indefining these components, their liquid and gaseous conditions arerelated to standard temperature and pressure. Although part of thecharge will be in the gas phase, and the mixture could more properly bedesignated as "fluid" instead of liquid, it is primarily a liquid chargeand for convenience is discussed as such. By any definition it is not asolid.

The liquid component is selected to be environmentally acceptable,nontoxic to humans, and stable. This component should not include anyelement or radical which after reaction with nitrous oxide will produceharmful products. A saturated alkane compound which is liquid atstandard temperature and pressures is to be preferred. Primary andsecondary alkane alcohols with carbon between 1 and 4 are useful, withethyl alcohol the preferred substance because it is a "green" (i.e.environmentally benign) substance. It is non-toxic (can be denatured),and with nitrous oxide primarily produces carbon dioxide, and nitrogen,and water. Other suitable alcohols are primary methyl-, propyl-, andbutyl-alcohols, and isopropyl alcohol.

The gas component is nitrous oxide. It will be recognized that undersome circumstances at least some of this component will be liquified,and under all circumstances, some will be dissolved in a liquid. Stillthis component will be described as a gas.

The molar relationship will be selected with the time to first gas(TTFG), Rise Time and Peak Pressure and effluent gases in mind, as wellas the production of fewest other compounds.

While the molar proportions of the liquid component to the gas componentcan vary from between about 10:90 to about 90:10, and some water can beincluded, the preferred charge is about 20% liquid component to about80% nitrous oxide by weight. Water (which is not considered part of theliquid component herein) can be added to vary the proper ignition point,pressure rise time, and volume of gas to be produced, and the ratio ofthe two reactants can be varied along with it. Water will rarely beadded in an amount greater than about 40% of the total charge. Wateracts as a burn suppressor and varies the rate of the reaction.

As the mixture becomes richer in the liquid component compared to thegas component, especially beyond about 40% by weight, carbon, methane,hydrogen, carbon monoxide and ammonia begin to appear as pollutants. Thepreferred ratio is stoichiometric of about 20% by weight of the liquidcomponent to about 80% by weight of the gas component.

A suitable charge by weight is 14.1% ethyl alcohol, 80.9% nitrous oxide,and 5% water. The preferred ratio of alcohol and nitrous oxide is14.85:85.15 (without water).

About 0.3 grams of charge per liter of inflated bag volume, plus orminus about 15% to adapt for special requirements is suitable. A typicalpassenger side air bag will require about 30 grams of charge, and thedriver side about 15 grams. The amounts for side impact bags is highlyvariable because of varying sizes and applications. Many will requireabout 5 to 10 grams.

The initiation of these charges is very rapid--in small fractions of asecond. As shown by FIG. 1, the peak pressures in the combustion chamberare very high.

The inflator 15 shown in FIG. 2 is intended to operate in the regime oftrace 11. It includes a body 16 having a heavy wall 17. A combustionchamber 18 is formed by wall 17. A metal fill tube 19 is welded to thebody, and when the combustion chamber is filled with the charge, it canbe pinched closed and sealed, such as by welding.

Body 16 includes a mounting flange 20 which can be attached to aplatform or partition 21 by screws 22. The flange is pierced by aplurality of flow ports 23.

A cap 25 is fixed to the flange and forms a flow channel 26 leading toports 23.

A burst tube 30, conveniently made of a material such as copper alloy iswelded to the body and forms a continuation of the combustion chamber. Aburst portion 31 is formed in the wall of the burst tube, which willburst under sufficient pressure. It is shown burst in the drawing. It isstrong enough to resist the storage pressure without bursting. Portion31 can be formed by thinning the wall of the tube or by notching it, forexample.

Initiation means 35 is mounted to the cap and communicates with theburst tube, and thereby with the rest of the combustion chamber. It ispossible to utilize a conventional pryotechnic squib for initiation, butthe advantages of a completely green system would be lost. Instead, andpreferably, a hot wire or exploding wire will be used. These are wellknown devices in which the wire is heated or exploded by the passage ofa large current such as can be stored in a capacitor. These devices arenot subject to the effects of stray currents or electrical interference.

Optional baffles 36 (which would extend around the burst tube) can beprovided to give an extended residence time in the inflator before thegases enter the air bag. The further expansion will cool the gases, andthe additional time can assure full combustion before the gases enterthe air bag.

An air bag mounted to vehicle structure will receive inflator gas fromflow ports 23.

Of critical importance in this embodiment is a nozzle 40 located in thecombustion chamber on the opposite side of the burst portion from theinitiator. It is this nozzle that causes this embodiment to function inthe high pressure-low temperature regime of trace 11.

When the charge is initiated, the combustion front will proceed from theinitiation means, past the burst portion, and to and through the nozzle.Pressure will quickly burst the burst portion (as shown), and the gaseswill begun to flow through the open burst portion.

The combustion front passes through the nozzle, and moves through thecombustion chamber. Because of the nozzle, the flow from the combustionchamber will be retarded, which results in a very high combustionchamber pressure.

The nozzle is proportioned so as to control the expansion ratio of anadiabatic expansion of the gases to the air bag pressure. In doing so,the temperature of the gases is profoundly reduced. The disadvantage ofhaving to withstand such a large combustion chamber pressure is offsetby the fact that It produces a low expanded gas temperature, andtherefore usually will not require any auxiliary means to cool the gasesbefore they are injected into the air bag.

The embodiments of FIGS. 3 and 4 function in a different mode, which isexemplified by trace 13. These are examples of the low pressure-hightemperature regime.

FIG. 3 and 4 are identical in concept, but are configured for differenttypes of installations. The inflator of FIG. 3 is round and flat so asto fit in a compact region such as a steering wheel, or in a side panelwhere there is little depth to receive it.

The embodiment of FIG. 4 is elongated, and can be used where there isample room for it. Passenger side installations are an example for theuse of the device of FIG. 4.

Inflator 50 (FIG. 3) includes a housing 51 comprising a base 52 and acover 53. A plate 54 is held between the base and the cover. It has aplurality of flow ports 55 which interconnect a first plenum 56 to asecond plenum 57. A flow port 58 in the base provides for exit of gasesto an air bag (not shown).

A spirally-wound tube 60 is placed in the first plenum. A first end 61of the tube is fixed to the base in communication with an initiator 62that is also fixed to the cover. The tube has a central passage whichforms a propellant tank 63. The second end of the tube is closed, so thepropellant tank can store the charge at an elevated pressure.

The wall of the tube includes a burst portion 65. As in the embodimentof FIG. 2, this is a weakened or reduced portion which will burst as theconsequence of the elevated pressure generated by initiation of thecharge. The burst portion is disposed in the first plenum close to, butspaced from, the initiator. The major portion of the combustion chamberis on the opposite side of the burst portion from the initiators.

The construction of FIG. 4 is generally similar. This inflator 70 has atubular housing 71 with an initiator 72 at a narrowed end.

An elongated tube 75 with a dimension of length and diameter, and also awall thick enough to resist the intended pressures is connected to thehousing. Conveniently it may be made of a copper alloy. A burst portion76 is provided near the initiator.

The combustion chamber 77 is the lumen of the tube. The free end of thetube is pinched shut and may be welded or otherwise permanently closed.

As in the embodiments of FIGS. 2 and 3, the ratio of length to diameterof the combustion chamber should be greater than one.

The tube may be helically wound to fit in the housing. The housing canbe provided with mounting means such as an external thread 80 formounting to structure of the vehicle.

The housing forms a plenum 81 into which the gases expand and from whichthey flow to an air bag (not shown). This plenum provides for furthercooling of the gases. While combustion is expected to be completed inthe combustion chamber, the plenum provides a region in which completecombustion can be assured.

The housing has an open end 83 for the gas outlet. This does permit anaxial thrust to be exerted by the housing. Should this be undesirablefor the existing gases, side ports may be provided with end 83 closed,so there will be no net thrust.

There are circumstances in which multiple bursts of gas into a singleair bag are desirable, or at least their availability. One example isafter the air bag is initially inflated at the moment of first impact.This inflation is generally quickly followed by deflation. However, ifthe vehicle rolls or is somehow struck a second time, additional air bagprotection may be needed. Another example is the desirability to exert adifferent rise rate of pressure, and even of ultimate maximum pressureon the passenger depending on his weight. Greater protection is neededfor a three hundred pound man than a sixty pound youth, and the standardinflation may not be suitable (and is not optimum) for both.

A simple solution would be to provide two inflators, separate from eachother, to be triggered by different events or circumstances. A problemhere is that after impact, one of the inflators may not have beeninitiated, and will remain in place as a possible risk for repairmen ordismantlers. While the compounds used in this invention are harmless,and if a hot wire initiator is used, it is invulnerable to heat, it isbetter practice to have the entire installation disabled, rather thanonly partially. This invention enables sequential bursts from a singleinflator source, which when initiated can provide only a single burst ora plurality of bursts, depending on the event, but after a firstinitiation has occurred, and all events have subsided, there remains nouncombusted material.

An inflator 150 for this purpose is shown in FIG. 5. In this device, ahousing 151 contains a combustion chamber 152 in the form of anelongated tube whose wall 153 includes a first burst portion 154. Thisburst portion fractures when a suitable pressure is exerted in thecombustion chamber. This embodiment is interesting because itscombustion chamber is provided with a second burst portion 155 near theother end of the chamber. A first initiator 156 is disposed at one endof the combustion chamber, and a second initiator 157 near the otherend. The burst portions are relatively close to their respectiveinitiators.

The combustion chamber is also the storage chamber for the charge, andboth burst portions discharge into the housing. A nozzle may be insertedinto the combustion chamber on the opposite side of either or both ofthe burst portions from the respective initiator, if desired.

When initiator 156 is fired, the charge will generate a pressure whichwill fracture burst portion 154 and discharge gas into the housing.

From the housing it flows through ports 159 to the air bag (not shown).If the second initiator is fired before the reaction is completed, asecond burst of pressure will be generated which will fracture thesecond burst portion. The result is a second burst of gas underpressure.

FIG. 6 is a somewhat more schematic presentation of this inventionwherein with only a difference in a single conduit, the device can beutilized for either the low pressure/high temperature regime, or for thehigh pressure/low temperature regime.

A combustion chamber 100 is bounded in part by a frangible burst portion101. It encloses an initiator 102 with appropriate leads 103. Apropellant reservoir chamber 104 (sometimes called an "auxiliarychamber") is connected to combustion chamber 100 through a conduit 105whose properties are critical to the selection of regime. A fill tube106 is provided in order to fill chambers 100 and 104 with themonopropellant charge.

An optional expansion chamber 107 receives gases from combustion chamber100, which in turn flow to gas bag 108.

A nozzle 109 for metering or cooling can be provided between chamber 107and the gas bag, if desired.

As to conduit 105, its dimensions will determine which of the regimeswill ensue after initiation. In the low pressure/high temperatureregime, auxiliary chamber 104 functions as a supply source forcombustion that occurs in chamber 100. For this reason, conduit 105 isdimensioned so as to permit ready flow of uncombusted charge intochamber 100 where combustion will occur. Accordingly, conduit 105 isprimarily dimensioned as a flame-suppressor, so that no flame front fromchamber 100 can enter chamber 104.

Thus, a swift and unrestricted flow of products of combustion flows intothe expansion chamber and into the air bag at a relatively hightemperature.

For operation in the high pressure/low temperature mode, the system isloaded with propellant the same as before, except that combustion isintended to occur in both of chambers 100 and 104. Accordingly, conduit105 is formed as a nozzle, and not as a flame suppressor. Whencombustion is initiated in chamber 100, the resulting flame front isintended to pass through conduit 105, and advance along chamber 104.Because combustion occurs in chamber 104, a high pressure is generatedin it. Conduit 105 meters the output pressure, and in so doing,profoundly lowers the pressure and the temperature of the gases. Thus inthe high pressure regime, chamber 104 acts as a chamber for combustion,rather than merely for supply.

In all respects other than conduit 105, the embodiments are alike. Ofcourse, when the high pressure regime is intended, the walls of chamber104 must be stronger than when the low pressure regime is intended.

The versatility of this invention provides for sequential bursts inresponse to multiple events. This arrangement can not only provide aplurality of bursts, but assures that no uncombusted material willremain, even if only a single actuation is required.

For this purpose, as shown in FIG. 7, there is provided a primarycombustion chamber 120. It is bounded in part by a burst portion 121. Aninitiator 122 is mounted in chamber 120. A conduit 123 connects chamber120 to an auxiliary chamber 124. Chamber 124 is provided with a filltube 125 through which the entire inflator is charged with propellant.

Secondary combustion chambers 130, 131 are connected to auxiliarychamber 124 through respective conduits 132, 133. Chambers 130, 131respectively include initiators 134, 135 and burst portions 136, 137.

All three burst portions 121, 136 and 137 form a barrier between theirrespective combustion chambers and an optional expansion chamber 138. Asillustrated, chamber 138 communicates with air bag 139 through anoptional nozzle 140, which can provide for metering or cooling of thegases before they enter the air bag. If preferred, the combustionchambers may exhaust directly to the air bag, without combining theireffluent gases; in a common expansion chamber.

In operation, the first burst will always be from primary combustionchamber 120. Conduit 123 may be dimensioned for either regime. Ifintended for the high temperature/low pressure regime, conduit 123 willbe proportioned to be a flame suppressor. Then auxiliary chamber 124will act as supply means for the primary combustion chamber.

As pressure reduces in the auxiliary chamber, propellant will flow fromthe secondary combustion chambers, into the auxiliary chamber and thenceinto the primary combustion chamber. If neither of initiators 134 and135 is fired, the monopropellant in both of them will be depleted andcombusted, and there will be no remaining propellant to constitute aresidual risk.

However, if during the very brief period involved, either or both ofinitiators 134 and 135 is fired, then the charge in that chamber will beinitiated and its respective burst portion will be broken. The generatedgases will then flow directly to the expansion chamber or air bag, andneed not pass through the auxiliary chamber or the primary combustionchamber. In this way, up to three simultaneous or sequential bursts canbe provided.

The primary combustion chamber and auxiliary chamber 124 can be used foreither regime by appropriately dimensioning conduit 123 as alreadydiscussed.

However, it is necessary that flame from the auxiliary chamber does notenter the secondary combustion chambers, because that would destroytheir capacity to respond to a subsequent initiation. For this reason,conduits 132 and 133 will be dimensioned as flame suppressors.

The exits from the secondary combustion chamber are significantly lessrestrictive to flow of gases than conduits 132 and 133.

It is undesirable to require that gases from the secondary combustionchambers pass through the primary combustion chamber.

In actual practice, the initiators will be disposed closely to the burstportions, so as to maximize the amount of combustion in the respectivecombustion chamber.

In practice, while the primary combustion chamber can operate in eitherregime, the secondary combustion chambers will function in the lowpressure/high temperature regime.

In FIG. 8 an inflator 210 includes a cup-shaped body 211 with a base 212and an encircling wall 213. A fill port 214 is formed through the base.

An end cap 215 is fitted to the open end of wall 213. A weld 216structurally joins the body and the end cap, and hermetically seals theinterior of the body.

A reaction chamber 220 is formed as a capsular enclosure by a cup-likebody 221 having a base 222 which abuts base 212. This base is preferablybonded to it by adhesives or by a weldment (not shown). Body 221includes a peripheral wall 223 whose open end is welded to the end capand abuts a circular flange 224 on the end cap. Thus the end cap and theperipheral wall form reaction chamber 220, and make a structural andhermetic seal for it. The fill port extends through base 222 intochamber 220.

Body 221 is made of a suitable metal, with several areas 225 of reducedthickness to provide frangible burst portions that fracture to open whenthe charge is ignited. Fracture is caused by the pressure of thegenerated gases. These areas may further be reduced by engravedpatterns, which eliminates the incidence of detached metal fragments inthe gas stream.

The spacing between walls 213 and 223 forms an expansion chamber 226 inwhich any incompletely combusted gases may complete their reaction andexpand to be cooled as appropriate. Optional annular baffles 227, 228may extend from the base and the end cap to provide a serpentine path,and to regulate, if necessary, the rate of reaction in the reactionchamber by causing a back pressure in the system.

If desired, patches 229 of a catalytic substance may be applied to theinside of wall 213 to catalyze the reaction of any unreacted components.

Nozzle ports 230 are formed through wall 213 of body 211. they will beclosed by a layer of burst foil 231 which will be blown out by theexiting gases.

To fill the reaction chamber with a gas-generating charge, a fill valve235 is threaded into the fill port. The fill valve is preferably weldedto the base to form a permanent and gas tight seal. The fill valve willbe of any desired type that enables the reaction chamber to be filledwith a liquid charge. After the charging is completed, the fill valvewill be permanently closed such as by welding it closed, or by sealingit with an epoxy or metal sealant.

An igniter 240 (FIG. 10) is fitted in an igniter port 241 in the endcap. A connector 242 is provided to connect the igniter with a source ofcurrent to initiate the reaction. In the preferred embodiment, a header243 is fitted and structurally and hermetically fitted to the end cap.It passes leads 244 and 245 to a bridge wire 246, which may merely be ahot wire, or instead may be an exploding bridge wire. Such header andwire constructions are well-known.

Instead of relying on heat or explosiveness of a wire, a thin film maybe connected between the leads which carries or consists of a conductivepyrotechnic which will heat and burn to ignite the charge.

Also, instead of leads and an electrical current, a window transparentto laser light may be placed in the header, and a charge through thewindow. Ignition may either be by direct absorption of the laser lightor by laser heating of a pyrotechnic in a film to autoignite the liquidpropellant.

It will be observed that the frangible areas in the reaction chamberwall are relatively close to the igniter, for a reason which will laterbe explained.

A flexible air bag 249 is schematically shown that is connected to theinflator to receive gases from the inflator, thereby to be inflated.

The embodiment of FIGS. 8-10 is most suitable for a driver sideinflator, because it is rather squat and can fit into a compartment inthe steering wheel. However, for a passenger side installation theheight limitation is not as severe and a thinner and longer constructionmay be made which is more convenient in these locations and which hassome advantages of its own. Because most of their parts differ only inrelative diversions, the description of the device in FIG. 11 will bebrief.

An inflator 250 includes a cup like body 251 and end cap 252 which arejoined and respectively include a fill valve 253 and igniter header 254.A tubular body 255 forms a reaction chamber 256 into which both the filltube and header open.

Nozzle ports 257 are formed through body 251, closed by a burst foil258. Frangible portions 259 are formed in the wall of body 255. Aflexible air bag 259a is shown connected to the inflator.

The principal difference between the embodiments of FIGS. 8 and 11 is aring-shaped baffle plate 260 extending across expansion chamber 261 withbaffle ports 262 therethrough. Notice again that the frangible areas areclose to the header. The header carries igniter means as alreadydescribed.

Notice that in this invention there is no separate initiator charge. Allignition occurs primarily in the reaction chamber and withoutparticipation by any other substance, such as hot gases from aninitiator charge. The charge is complete, and when initiated itsreaction is self-sustaining. Further, because there is a substantiallength of charge from the initiator, and the frangible ports are closeto the initiator, the reaction face of the charge will recede from theigniter and from the ports. Its gaseous products will exit through thoseports and little or no liquid is exposed to require reaction in theexpansion chamber (or in the air bag). No means is needed to expel theliquid charge, because the reaction chamber is closed beyond theseports. Accordingly, in contrast to other known devices that use liquidcharges, it is intended that reaction primarily occurs in the chamberwhere the charge is stored. This significantly reduces the bulk andcomplexity of the device, because it is not necessary to provide asubstantial volume in which reaction occurs, for reaction beyond thestorage means (which in this invention also functions as the reactionchamber).

This invention is not to be limited by the embodiments shown in thedrawings and described in the description, which are given by way ofexample and not of limitation, but only in accordance with the scope ofthe appended claims.

We claim:
 1. A gas generator to provide gases under pressure forinflating an air bag, comprising:a capsular enclosure forming anunobstructed combustion chamber, said enclosure having a wall with afrangible burst portion which fractures upon the exertion of asufficient gas pressure in said combustion chamber; an initiator insidesaid combustion chamber for initiating, inside said combustion chamber,the combustion of a charge contained in said combustion chamber; aliquid gas generating charge contained in said combustion chamber whichis auto-ignitable by said initiator, and whose- reaction isself-sustaining after ignition; said frangible burst portion beingdisposed between said initiator and a major portion of said charge,whereby upon ignition said charge generates a gas pressure to open saidburst portion, and the reaction progresses into the chamber on theopposite side of said portion from said initiator, said reaction beingsubstantially completed inside said combustion chamber; and a nozzlefitted in said combustion chamber on the opposite side of the burstportion from the initiator, and closer to the burst portion than saidmajor portion of the charge so as to limit the ratio of flow ofcombustion gases to the burst portion.
 2. A gas generator to providegases under pressure for inflating a vehicular air bag comprising:acapsular enclosure forming an unobstructed reaction chamber, saidenclosure having a wall with a frangible portion therein which fracturesupon the exertion of a sufficient gas pressure in said reaction chamber;a non-pyrotechnic initiator inside said reaction chamber; fill meansthrough said wall to enable the injection of a liquid charge into saidreaction chamber and to retain it therein; a liquid gas-generatingcharge which is autoignitable by said non-pyrotechnic initiator, andwhose reaction is self-sustaining after ignition; said frangible portionbeing disposed between said initiator and a major portion of saidcharge, whereby upon ignition said charge generates a gas pressure toopen said portion, and the reaction progresses into the chamber on theopposite side of said portion from said initiator, said reaction beingsubstantially completed inside said combustion chamber; and said chargecomprising ethyl alcohol and nitrous oxide, the molar ratio of thealcohol to the nitrous oxide being about 15:85 and being stored in saidreaction chamber at an elevated pressure such as to increase thesolubility of the nitrous oxide in the ethyl alcohol.